1. Field of the Invention
The apparatus of this invention resides in the area of bar descalers and coil descalers and more particularly relates to blast machines which propel particulate materials at reinforcement bars (rebars) or other cylindrical items and in another embodiment against wide sheet metals in order to clean them so that they are in suitable condition for further processing such as the application of coatings and the like.
2. Description of the Prior Art
Rod material such as reinforcement bars commonly called rebars frequently require cleaning and descaling to remove oxide particles caused by rust or other substances that may be formed or caked thereon. Such cleaning is frequently mandated by the laws of various communities where, for example, rebars are used in concrete road and bridge construction. It has been found that when uncoated reinforcement bars are used in road and bridge construction and the roadway cracks, salt water will seep in and electrolysis will take place causing the rebars to rust, weaken, decompose and precipitate premature deterioration of the roadway or bridge. To avoid such deterioration, various states have created laws requiring that rebars must be coated with a water-impervious material that will prevent them from rusting. In order to coat the rebars, the rebars must be first cleaned which is usually accomplished by shot-blast techniques where the rebar is struck by shot propelled at high speed against the rebar thereby cleaning the bar.
In the prior art to accomplish such cleaning, rebars are usually conveyed through a shot-blast machine on V-groove rollers. Such machines are frequently approximately 20 ft in length and require a pit thereunder of approximately 8 feet in depth. Such blast machines frequently present problems in that the rebars, being carried on the V-groove rollers of the conveyor which moves them through the blasting area where shot is propelled against the bars, will tangle from time to time requiring the shutting down of the machinery and time-consuming and expensive cutting up of the bars to remove the tangled bars from the machinery. Such machines are also costly to maintain and require substantial parts replacement since the shot that is propelled against the rebars carried on the V-groove conveyor rollers also hits the conveyor rollers and gradually destroys the conveyor roller assembly which must then be replaced, requiring shutting down of the assembly. Further, the 8 ft pit that is required for prior art machinery is costly to dig and incorporate into production lines.
In another embodiment of the prior art, machines have been utilized to clean sheet metal which usually comes in coils and is descaled by delivering it on conveyors through long machines which have shotblast wheels disposed above and below the sheet metal being cleaned. Such machines usually have a plurality of shotblast machines disposed in a large long chamber through which the sheet steel is delivered wherein each shot blast machine cleans a specific portion of the upper or lower surface of the sheet steel. Some of the prior art cleaning machines have the lower blast wheels disposed at 45 degree angles to the steel sheets being cleaned. When cleaning sheet material, two problems have arisen. The first is that the shot tends to accumulate on top of the sheet as it passes through the cleaning chamber, the chambers being as long as 20 feet and this accumulation can create a considerable problem at the time the sheet steel exits the chamber for further processing. The second problem is deformation or warping of the sheets caused by the blast machines of the prior art in that they have hot spots in their blast pattern which unequal blast intensity causes such deformation. In the prior art to remove the shot from the top of the sheet, two methods have generally been utilized. The first method incorporates a series of brushes that sweep horizontally to the side to try to brush the shot material off the sheet steel but in some cases this method has been found insufficient and the shot will pass out of the chamber on the top of the steel which occurrence is undesirable. Another method which has been used provides blowers at the exit of the chamber, blowing back into the chamber parallel to the direction of the workpiece flow to try to blow the shot off the top of the steel, but this method has also proven to be less than one hundred percent effective in that many times more shot will be deposited and left on top of the steel sheet than the blowers can effectively remove.